A number of processes for purification of off-gases and exhaust gases produced from various thermal power plants are known in the art. Such gases contain undesirable components, such as NOx (nitrogen oxides including NO, N2O3, NO2, N2O4, N2O5, etc.), sulfur oxides, and the like. These processes are based either on absorption of such impurities by liquid absorbents, or on their conversion (reduction) into harmless compounds (e.g., water vapor and nitrogen in the case of NOx reduction). The most widely employed processes for reduction of NOx use ammonia and selective catalytic reduction (SCR). The SCR processes make it possible to carry out the reduction of NOx to elemental nitrogen and water vapor in the presence of oxygen contained in the off-gases. See U.S. Pat. Nos. 5,401,479; 4,859,439; 4,855,115; 4,789,533; 4,438,082; 4,720,476; 4,695,438; 4,732,743; 4,975,256; 4,521,388; 5,401,478; and 5,753,582, the entire subject matter of which is incorporated herein by reference. After off-gases are cleaned of minor impurities by conventional processes/equipment, they are vented to the atmosphere.
Moreover, there are also known processes for purifying various commercial grade gases, such as inert gases. For example, U.S. Pat. No. 4,579,723, the entire subject matter of which is incorporated by reference, utilizes a multi-step catalytic process to remove CO, CO2, H2, H2O, and O2 from an argon gas.
Various processes have been utilized for removing O2 from very pure nitrous oxide gas produced from stand alone commercial processes for subsequent use in semiconductor manufacturing. In Japanese Kokai No. 06016402, oxygen is removed from commercially produced nitrous oxide using a manganese oxide catalyst. However, oxygen is removed by using oxygen present in the gas to oxidize the catalyst from a lower to a higher manganese oxide, which does not involve catalysis of reactions involving oxygen containing gases to form easily removed products.
Heretofore, removal of impurities from nitrous oxide off-gases has not been contemplated. Releasing nitrous oxide off-gases into the environment is a source of pollution and a waste of nitrous oxide that, if economically and feasibly separated from such off-gases to provide a commercial grade nitrous oxide source, could lead to its use in various processes, such as for use in conversion of benzene to phenol by hydroxylation. See U.S. Pat. Nos. 4,982,013; 5,001,280; 5,055,623; 5,110,995; 5,672,777; 5,756,861 and 5,808,167, the entire subject matter of which is incorporated herein by reference. Accordingly, there is a need in the chemical industry for a process that purifies nitrous oxide off-gases and at the same time commercially and economically produces nitrous oxide suitable for various commercial applications.